It is also possible we are in a local optimum and there are huge performance or efficiency or other kind of gains available, but to realize them investments in radically different architectures need to be made, and those are not economical while existing approaches can be improved.
This is exactly my perspective. Existing ISAs have a de facto stranglehold on the mindset around computer architecture because they could provide a consistent foundation while the underlying implementation got better and better faster than anyone could build something on top of it.
There have been plenty of small experiments in other architectures but never enough of a mindshare investment to really evaluate viability and performance of alternatives. There are costs to a more diversified architecture eco-system, sure, but I fully believe we will find more value in that space than we have so far taken advantage of.
